Abstract

The Cherokee Ridge arch is an east–west-trending structure that separates the Washakie Basin of south-central Wyoming from the Sand Wash Basin of northwestern Colorado. It is characterized by a distinct east–west-trending lineament on Landsat images and a zone of northwest–southeast-striking, en echelon, high-angle faults that cut Upper Cretaceous to Miocene sedimentary rocks. The lineament is interpreted to be the surface expression of the Cheyenne belt, a buried suture zone that separates Proterozoic crust of the Colorado province from Archean crust of the Wyoming province. Results of this study indicate that the surface and near-surface structures along the Cherokee Ridge arch are the result of periodic strike-slip motion along the Cheyenne belt since Late Cretaceous time and possibly before. Previous structural and paleomagnetic studies support the conclusion that left-lateral transpressional motion occurred during the Late Cretaceous and early Tertiary as the area was under the contractional tectonic regime of the Laramide orogeny. The left-lateral shear zone is interpreted to be a lateral ramp accommodating west-directed thrusting that culminated in the formation of the Rock Springs uplift as the Colorado Plateau rotated in a clockwise direction at the end of the Laramide orogeny. A significant amount of vertical reverse displacement would also have occurred at this time along the south-dipping shear zone, giving the arch its present-day structural relief. This interpretation is also consistent with uplift of the Uinta Mountains during the Eocene. Right-lateral transtensional motion is interpreted to have taken place after the Miocene as the Colorado Plateau rotated to the west relative to the more stable Wyoming province during Tertiary extensional events. Northwest translation of the Colorado Plateau during Cenozoic extension is also supported by structural and paleomagnetic studies. Most surface structures observed along the arch are related to this most recent period of wrenching.